Method for preparing explosives



July 9, 1957 PERCENT YIELD OF CYCLONITE o 5 l 8 BACHMANN 2,798,870

METHOD FOR PREPARING EXPLOSIVES Filed July 16, 1943 REACTION TEMPERATURE-(DE.GREES CENTIGRADE) Warner E E2 achmann United States METHOD FORPREPARENG EXPLQSIVES WernerEnBachmann,Ann Arbor, Mich, assignor to theUnited Statesof America as'representad by the taryof War ApplicationJuly 16, 1943, erial No. 495,078

11 Claims. (Cl. 260-448) O2NN N 1\|IO2 and therefore,on-thisassurnption, its systematic chemicalname iscyclotrimethylenetrinitramine. It has also been variously calledHexonite, Hexogen, T4, C6, andcyclonite. As a matter of convenience,however, theterm Cyclonite will hereinafter be used .to'designate thismaterial.

The explosive in question appears to have been discovered by .Henning(D. R.P. 104,280,.June 14, 1899), who prepared it by convertinghexametnylenetetramine (hereinafter called "hexamine), tothe-corresponding dinitrate an'd then a'ddingthe dried dinitrate tocold, very concentrated nitricacid. 'For' a number of years littleinterestwas shown in the new explosive. However, when the *developmentdfsyntheticmethanol opened thedoor to-explosives basedon'formaldehyde,interest in cyclonite was "renewed, and between 1919 and 1921, von Herz(DJR. P. 298,539 and 299,028; G. B. 145,791; Swiss 88,750; U. S.1,402,693) disclosed a so-called direct nitration (nitrolysis) method ofpreparingcyClonitebY treating hexamine directly with cold, concentratednitric acid, according "to the scheme indicated below and referred toherein as Scheme 1 or Equation 1:

characterized by a number of significant disadvanages.

Inithe firstplace, althoughonlyrthreemoles of nitric acid Cir aretheoretically required by Equation 1, in actual practice a very largeexcess of nitric acid (from 20 to 25 molesper mole'of. hexamine) isrequired to obtain yields of 'to (See, for example, Hale, Jour. Amer.Chem. Soc., 47, 2754 (1925).) In the second place, the reaction isfrequently accompanied by a violentfume-otf which renders large scalemanufacture hazardous and diificult to control. Thirdly, that portionofthe hexamine molecule which is represented in theprojection formula asin the middle of the ring (the so-called central part of the hexamine)represents one-half (3 moles) of the six moles of formaldehyde requiredfor the preparation of the hexamine. This half-equivalen of formaldehyderepresented by the central part appears to he completely wasted in thedirect nitration process, througheventual conversion to carbondioxideand other. reaction products. Moreover,the loss of thehalf-equivalent of formaldehyde is attended by a reduction of a largeamount of nitric acid to N204. Accordingly, in large scale manufacture,a very large proportion of the equipment is representedbyapparatus forthe recovery of nitric acid and the oxides of nitrogen, and even thoughthis recovery apparatus may obviate serious nitrogen loss, it will beapparent that the formaldehyde which is oxidizedto'COz isirretrievably'lost. Accordingly, theloss of the halfequivalent offormaldehyde per mole of hexamine, and the enormous nitric acidrecoveryproblem, constitute the main defects of the direct nitratioifprocess.

Despite the many disadvantages of the direct nitration processes, forover forty years the foregoing degradative procedures ofHenning and ofvon Herzappear to have been the only known methods available forcyclonite production. Within recent times, however, a synthetic methodhas been described by schiessler and Ross inULS. application Ser. No.444,254, filed May 23, 1942. This method (which is known as theso-called M'cGill Process) involves the treatment of formaldehyde (e. g.in .the form of paraformaldehyde) with ammonium nitrate at 60 to 85 C.in the presence of a dehydrating agent (e. g., acetic anhydride)according to the overall Equation 2:

By the foregoing method, cyclonite may be obtained in yields as highas50 to 55% of the theoretical, based on the material balance indicatedby the overall Equation 2.

Now, as indicated in connection with Scheme 1, in the degradativenitration process, thethree moles of formaldehyde (represented by thecentral part) are destroyed per mole of cyclonite produced. On the otherhand, in the more recent Schiessler'and Ross synthetic method, threemoles of formaldehyde are required per mole of-cyclonite produced(Scheme2).. It was accordingly of interest to determine whether theformaldehyde lost in the degradative nitration" process, could beusefully employed in the synthetic process. This proposal neglectedimportant considerations of mechanism, since the wasted formaldehyde inthe direct nitration process appears as certain formaldehyde-nitrationproducts, and ultimately as CO2, rather than asformaldehy'de.Nevertheless, prior investigators carried out the direct nitrationprocess in the presence of ammonia donors (e. g,, ammonium nitrate) inthe hope that the wasted formaldehyde might combine with the ammoniadonor to reform 'hexamine and thus .be returned to the main reaction.The results, howexer, gave little encoura'ge ment thatsuch a processwould effect an appreciable improvement in yield, and indicated that thereaction prod uctsof the lost half-equivalent of formaldehydewould 3 notcombine with ammonium nitrate in the presence of strong nitric acid toyield cyclonite.

The object of the present invention is to provide a new and improvedmethod of preparing cyclonite from hexamine, whereby two moles ofcyclonite are theoretically obtainable from one mole of hexamine, andwhich actually produces in excess of one mole of cyclonite per mole ofhexamine.

A further object is to provide What may loosely be termed a combinationprocess wherein both the degradative and synthetic processes of theprior art may be considered as taking place concurrently.

Another object is to provide a process which is capable of producinghigher actual yields of cyclonite per mole of hexamine-assuming optimumconditions and yields in each case-than the aggregate yield obtainableby first carrying out the direct nitration process on one mole ofhexamine, and then separately carrying out the McGill process, startingwith paraformaldehyde in an amount equivalent to all the formaldehydelost in said direct nitration process.

A further object is the provision of a process for preparing cyclonitewhich obviates the enormous nitric acid requirements of the directnitration process and which requires much less acetic anhydride than theMcGill process.

Still another object is a method of preparing cyclonite which requiresless ammonia and formaldehyde equivalents per pound of cycloniteproduced, than any previously known method.

Other objects and advantages will be apparent as the invention ishereinafter more fully described.

As a result of an extended investigation, it has been found that theforegoing objects and advantages may be attained by the process of thepresent invention, which involves the treatment of a hexamine compoundwith an ammonia donor and nitric acid under conditions effecting theelimination of the elements of water, the reaction being carried outunder certain critical temperature con- 'ditions, as hereinafterexplained.

The hexamine compound mentioned in the preceding paragraph may consistof hexamine itself, or a hexamine derivative such as a hexamine salt,for example, hexamine acetate, hexamine mononitrate, hexamine dinitrateand the like. The ammonia donor preferably consists of ammonium nitrate,although other ammonium salts such as the acetate and similar equivalentmaterials may be employed if desired. The elimination of the elements ofwater is elfected in the presence of a volatile fatty acid anhydride,such as a lower fatty acid anhydride, for ex ample, acetic anhydride,propionic anhydride, butyric anhydride and the like, which combines withthe eliminated water.

The conditions prevailing when the foregoing reactants are broughttogether, exert an important influence on the course and extent of thereaction. As a matter of convenience, these conditions may be classifiedas (1) preferred proportions of reactants and (2) critical ranges oftemperature at which the reaction may be carried out.

Considering firstly the preferred proportions of reactants, it has beenfound that the optimum conditions for the reaction approach thoseindicated by the theoretical material balance of the overall equations,which (in the case of hexamine and hexamine dinitrate) may be written asfollows:

(3) Hexamine+4HNO3 2NH4NO2 6(RCO)2O=2 cyclonite+ IZRCOOH (4) Hexaminedinitrate+2HNOs+2NH4NOs+ 6 (RCO)2O=2 cyclonite-l-IZRCOOH In most cases,an excess of nitric acid, ammonia donor and dehydrating agent over thetheoretical amounts required by the overall Equation 3 or 4, are usuallydesir- 'able. Thus when hexamine itself is employed, excellent yields ofcyclonite (over 75% of the theoretical, based 4 on Equation 3, supra)may be obtained using approxi mately 2.3 to 3.2 moles of ammoniumnitrate, 4.5 to 5 moles of 98% nitric acid and 6.8 to 8.0 moles ofacetic anhydride per mole of hexamine. Likewise with hexamine dinitrate,excellent yields (over 80% of the theoretical, based on Equation 4,supra) may be obtained using approximately 2.3 to 3.2 moles of ammoniumnitrate, 2.4 to 2.8 moles of 98% nitric acid, and 6.8 to 8 moles ofacetic anhydride per mole of hexamine dinitrate.

While the foregoing proportions are preferred, satisfactory yields ofcyclonite may be obtained over a wide range of operating conditions,particularly if the reaction temperature and time are varied to suit theparticular proportions of reactants selected for carrying out thereaction. Thus for example, Table I gives illustrative ranges for eachof the reactants, which may be used to give satisfactory yields ofcyclonite when the reaction is carried out at about 6075 C. For optimumyields, particularly where it is desired to lower the consumption ofreactants, the ammonium nitrate and nitric acid are preferably reducedroughly in the same molecular proportions.

TABLE I. MOLAR PROPORTIONS OF REACTANTS Hexamine Nitric Acid AmmoniumAcetic Anhy- (98%) Nitrate dride 1 4 to 6 2 to 4 (or more) 6 to 8Hexamine Nitric Acid Ammonium Acetic Anhydinitrate (98%) Nitrate dride 12 to 4 2 to 4 (or more) 6 t0 8 It will thus be evident that a Widechoice in the proportions of reactants is available to the operator incarrying out the process of the present invention. Moreover, nitric acidless concentrated than 98% (e. g., 70%) may be employed, providedadditional anhydride is used in an amount equivalent to the Waterpresent in the less concentrated nitric acid.

Before leaving the discussion of reactant proportions, it is deservingof emphasis that all four reactants (i. e., hexamine compound, ammoniadonor, nitric acid and fatty acid anhydride) appear to be essential tothe reaction. If any one of these four is omitted, substantially nocyclonite is obtained. Thus, in one experiment where ammonium nitratewas the only reactant omitted, substantially no cyclonite was producedat C., although it might be expected that at this temperature the directnitration reaction might take place between the hexamine and the nitricacid. Such however, does not appear to be the case, except to a verylimited extent (e. g., about 2%). Accordingly, all four reactants areconsidered necessary to the production of cyclonite by the process ofthe present invention.

Referring now to the critical temperature for the prep aration ofcyclonite, there is, in general, an unusually narrow minimum temperaturerange for each specific set of reaction conditions (e. g., proportionsof reactants, time of reaction and details of procedure). If theproportions of reactants or the time of treatment or the details ofprocedure, are changed, this narrow minimum temperature for cycloniteproduction may shift somewhat. Generally speaking, however, the minimumtemperature range for appreciable cyclonite yields will be found to liesomewhere above approximately 35 C. to 40 C.

The foregoing general principles may best be illustrated by reference tothe single figure of the appended drawing which is a graphicalrepresentation of the effect of time and temperature changes oncyclonite yiel d when the reaction is carried out in all cases with thesame proportions of reactants and the same general procedure. Curve S(solid line) shows the effect of temperature on yields of cyclonite whenthe reaction time is relatively short (12 /2 minutes). Curve L (brokenline) shows the temperature etfectzwhen the reaction time-is-relativelylong} (45 minutes). Ineach case thereactantswerei used. in the followingproportions: hexamine, 33.6 g.; nitric. acid (98%), 75 g.;ammoniumnitrate, 55 g.; and acetic anhydride, 180 cc. Except for thevariations. indicated, the procedure in all cases wassubstantiallyotherwise identicalv with that described hereinafter in. connection withExample IV.

By inspection of the two curves shown inthedrawing. it will beevident.thatthe effect of temperature on the yield isiunusually pronouncedinbothminstances. Moreover, in the case of the relatively short reactiontime (curve. S) the minimum temperature appears to lie above 40?C.,.whereas forthe relativelylong reaction time, thenriuimum lies aboveabout 35 C.

It should be noted that the. temperature-yield relationship shown intheJdraWing. applies, strictly speaking, only to the-particularproportions of reactants (mentioned above) which were maintained inobtaining the data for thegraph.v If the proportions of reactants, orthe time of treatment, or both are modified, the curve maybe somewhatdisplaced to the leftor right on the horizontal 'axis, and theshape ofthe curve may also be alteredi Thus an increaseinthe reaction time tendsto raise thewyields at the lower reaction temperature. However, the-graph* gives .a. general picture of the pronounced eifectof-temperature on the yield for any specific reaction condition.Moreover, ittappears generally to be true that the mini-- mum criticaltemperature for cyclonite production lies" somewhere :above about 35 to40 C.

If the reaction is carried out below this minimum tem-- perature range(forexample, at -35 C.) theprincipal reaction'productisusually asubstance melting at about 154 C. which appears to have at leastloneacyl" group inthe molecule. At temperatures somewhat above theminimunrrange given above, cyclonite will'be obtained in varyingyieldsdepending'on the time of reaction and proportions of reactants used.Thecyclonite-so obtained may contain the above low-melting impurity toavarying but usually small degree, depending on the precise conditionsobtained during the reaction. This impurity, however, is readily removedby digesting the unneutralized reaction mixture with water at 90100 C.for 1 /2 to 12 hours, which converts the low melting compound to'watersoluble and volatile products without, however,detrimentally-altectingthe cyclonite. If the preparative reaetion iscarried out at temperatures 15 1030" above tov C. the amount oflow-melting impurity is consider ably decreased, while the yield ofcyclonite improves. Thus the optimum temperature range for cycloniteproduction appears to be between to 90 C., and for commercial'operations to C. willusually betound 'to' be most satisfactory.

"in regard toa possible ceiling. reaction temperature forcyclonitepreparation, as the temperature increases, theyield and quality of thecrude cyclonite may-fall. offsomewhatat temperatures above about C.Cyclonite has, however, been obtainedabove this temperature (e. g., C.).The actual maximum-temperature at which cyclonite is to be producedshould be determined withreference to safety considerations, and fromthis point of view onehesitates to run the reaction above C.

In: addition to the low-melting, readily removable byproduct mentionedabove, the cyclonite produced by the process of the present inventionmay also contain. a highmelting compound (M. P. about279-280 C.) invarying amounts (up to 10%, forexample), depending'on the proportionsand conditions employed. This compound, however, appears to be anexplosive substance quite'similarto cyclonite in explosive power andbrisance, and is be-' lievedto be ahomologue of cyclonite (i. e.,cyclotetra methylenetetranitramine) fOt'lWhlCh reason it mayconveniently be. designatedflby thev trivial term, homo-' cyclonite.Regardless of its structure, the presence-ofi homocyclonite. in the.cyclonite. produced. byrthe process: ofthe present invention. is notobjectionable fromithepoint: of :view of ballistic power and.brisanceofthe productand: therefore homocyclonite is not to be regardedas 11111-3 desirable; impurity? in the cyclonite produced.=-by-'thepresent process. For this reason, .conditionswhidhfavorthe.formation of relatively high proportions ofhomocyclonite. (e. g., up to.10%) as a by-produc in cyclonite production .are not objectionable inrespect to the? explosive power of the product. Thesehomocyclonitefavoring conditions appear to include highanhydrideand. lownitric acid proportions.-

Where preferred; additional materials may be employed; for example, asreaction mediaor as solvents: for:one:or: more of the reactants. Thus,the mother liquor'from; a previous run may be used as a reaction media;or the -hexamine. may be: dissolved in a suitable inert solvent, forexample, .a substantially; anhydrous lower fatty acidlsuch' as.glaci'alacetie. acid. Moreover, .bytheuseof a hexamine':SOllltiOHiHJCOnjll'IlCtlOH with a suitable combinationof"theother-reactants; a procedure may be'employed wherein tall .thereactants are. charged totheareaction vessel. in: liquid/form.. Thus thehexamine may be dissolved in: acetic acidaand'thei ammonium nitrate inthe-'nitric-acid; withvacetie'anhydride. as the third in liquid, toprovide: ans allliquidafeedf modification within the ambit of 1 the:present-invention Thewdetails'of this all-liquid-feed? modification are.moreparticularly described and. claimed in the copendingapplieati'on ofGeorge F. Wright, Douglas: C. Downing and Henry-H. Richmond, SerialNo'.495,082,-. filed July 16,- 1943, issued as;Patent No. 2,434,879;Ian-1' uary; 20,1948;

In order more clearly to disclose: thevnature ofrthen presentinvention,, several illustrative embodiments: :will

hereinafterbe described in considerabledetail.

clearly be understood, however, that this is done solely bywayofexample, and-is-notto be construed as inany' manner limiting thespirit or scope of the appended claims;

Example I (SOLID AND LIQUID FEEDS, USING HEXAMLNE- DINITRATE) efficientmechanical stirrer, one for athermometentwm for burettes, and a large.flanged one for the addition of solid). The flask was placedin a waterbath not much larger irr diam'eter than itself. Thisbath was equippedwith a thermometer andcoul'd be heated by steam and cooled =by runningwater.

Three operators are desirable to regulate the" addition. and controlthe" temperature for the: reaction; Sixty-fives grams-ofhexamine.dinitratewas divided into 26 substarrtially equal portions (eachportion was weighed into atesti tube forconvenience. in handling); cc.of aceticanhydride wasplaced in a burette calibrated; in 26. substantially equal portions; and 26 cc. of 98% nitric.acicl was placed inanother burette calibrated in 28 substan-: tially equal portions.

At the beginning of the run, 50 g. of dry'ammonium nitrate-(60420 mesh)and 30 cc. of glacial'aceticacid.

wereplaced inthe flask. The temperature was raised to 75 C. and 30 cc.of acetic anhydride was addedflhis is The- 30 co. in addition to the 145cc. in the burette). resulting mixture was quite fluid andeasilystirred. Eflicient agitation is essential for optimum yields.

A-quarter portion of hexarnine dinitrate-was added'lto the mixture inthe flask. This serves to inhibittheviolent'l reaction between theacetic anhydride and thenitrc acid..

Two portions of nitric acid were then slowly added. The

third portion of nitric acid was then added simultaneously.

It should t er-portion for quarter-portion) over a period of abouttwelve-minutes. The temperature withinthe flask was maintained at 74-76C. throughout the addition. The first operator added the nitric acid andwatched carefully the inside and outside temperatures, regulating thesteam and cooling water. The second operator added the acetic anhydrideto correspond to the addition of the nitric acid and, watching thenitric acid burette, called off the addition in quarter-portions (i. e.,one-quarter, one-half, threequarters, all added). The third operatoradded the solid (hexaminedinitrate) to correspond to the addition of thenitric acid; he added a quarter of the contents of a test tube at atime. The addition of the liquids was continuous, and that of thesolids, effectively so (i. e., in 100 quarterportions).

After the addition was complete, the mixture was stirred for minutes atthe same temperature. The water bath was then removed and the mixturewas allowed to cool to 60 C. (about 10 min. were required). I It wasthen filtered through a warm, coarse Jena funnel. The first-crop productwas washed with 30 cc. of cold glacial acetic acid, and then with two 50cc. portions of hot water. The air-dried product was granular and ofgood appearance; M. P. l203 C. (corn) with previous softening; yield,81.1 g. or 75% of the theoretical, based on Equation 4, supra,representing an actual yield of about 1.5 moles of firstcrop, high gradecyclonite per mole of hexamine dinitrate. A second crop of less purecyclonite may be obtained by drowning the filtrate in an equal volume ofwater, then digesting the mixture for one hour or more at about 95 C.and cooling. In this manner, from 8 to 10 grams of less gpure cyclonite,melting at about 190-200 C., may be recovered from the filtrate.

desired to reduce the number of liquid feeds, the nitric acid may bemixed with the acetic anhydride. In this case however, thenitric-acid-acetic anhydride mixture should be prepared and used at lowtemperatures (e. g., 5-15 C.) as soon as prepared.

Example [I (SOLID AND LIQUID FEEDS, USING HEXAMINE INSTEAD OF THEDINITRATE) The apparatus was the same as that described above. 33.6 g.of hexamine, 43 cc. of 98% nitric acid and 160 cc. of acetic anhydridewere used. Addition of the reagents required about 15 minutes. Thetemperature was maintained at 73-77 C. during the reaction. Before theother reagents were added, 50 g. ammonium nitrate was placed in theflask together with cc. of the cool, clear mother liquor from a previousrun. The procedure was similar to that used in Example I. After portionnumber 5 of the other reactants was added, 25 g. of additional ammoniumnitrate was added to the reaction mixture. In a typical run, a yield of73% of the theoretical (based on Equation 3, supra) was obtained; M. P.(corn) 197-202 C. This represents an actual yield of approximately 1.46moles of first-crop cyclonite per mole of hexamine employed.v Asecond-crop may be obtained from the filtrate by the procedure describedin Example I. As in Example I, the second-crop cyclonite is less purethan the first-crop and may contain a relatively high proportion (e. g.,10 to 20%) of homocyclonite.

Example III (ALL-LIQUID FEED TO SUSPENSION OF AMMONIUM NITRATE IN A020,USING HEXAMINE INSTEAD OF THE DINITRATE In a 1-liter five-necked flaskequipped with a mechanical stirrer, a thermometer and three burettes,are placed g.) of 98% 65 g. of ammonium nitrate (granular or finelydivided) dried at 50 C. for 18 hours, and 60 cc. of acetic anhydride.The mixture is stirred and'heated in a water bath 75 C. (internaltemperature). To the hot mixture are added separately and concurrently,from the three burettes (Note 1, infra), cc. of 95 acetic anhydride, 43cc. (64.5 g.) of 98% nitric acid, and a solution of 33.6 g. of hexaminein 53 cc. of glacial acetic acid (Note 2, infra), during a period ofabout fifteen minutes.

The temperature is held at 7476 C. during additions. The reactionmixture is heated at 74-76 C. with stirring for five to fifteen minutesafter the reactants have been introduced. 'i

Without cooling, the mixture is diluted to a concentration of about 30%acetic acid by the addition of 675 cc. of warm water (60 C.) and thenheated on the steam bath (90-100 C.) with stirring for one totwenty-four hours. This digestion step destroys the low-meltingimpurities, as more particularlydescribed and claimed in my copendingapplication, Serial No. 495,079, filed of even date herewith, now PatentNo. 2,680,651.

The mixture is cooled to 20 C., with constant stirring, and filteredimmediately by suction. The white, glistening, sandy single-cropcrystals are washed with four 50 cc. portions of warm water (60 C.) andoven dried at 50 C. The yield is 76-79 g, or 71-74% of the theoreticalbased on Equation 3, supra, representing about 1.4 moles of cycloniteper mole of hexamine; M. P. 196- 197 C. (corn) with previous softeningat 191 C. The main filtrate (but not the washings) is reserved forrecovery operations.

In some instances better yields may be obtained with the above procedureif slight variations are made; for example, by adding some acetic acidand a small amount of the nitric acid to the acetic anhydride in theflask at the start of the reaction. Another alternative is to maintainthe above described reaction mixture at 54-58 C., rather than at 75 C.,with no other changes. The yields obtained with either of thesemodifications run as high as 82% of the theoretical, based on Equation3, supra.

Note 1.-In order to secure a uniform introduction of of the reactants inequivalent amounts, the three burettes were marked with calibrationscorresponding to 25 cc. portions of each reactant.

Note 2.This solution has a volume of about 75 cc. Since the solution isquite viscous and does not drain readily in the buette, it is convenientto pepare a small excess of the solution and determine the amountactually introduced by dilference in weight.

Example IV (ALL-LIQUID-F'EEDS, USING HEXAMINE INSTEAD OF THE DINITRATE)A yield of 70-90% cyclonite may be obtained by a modification of theprocedure described in Example III, which permits the use ofalHiquid-feeds. In this modification, the first liquid feed consists ofthe ammonium nitrate dissolved in the nitric acid with the formation ofa clear, water-white solution (after the evolution of oxides ofnitrogen). The second liquid feed consists of the hexamine dissolved inglacial acetic acid. The acetic anhydride constitutes the last liquidfeed.

Thus, a solution of 55 g. ammonium nitrate in 50 cc. nitric acid wasprepared and placed in one burette. In another burette was placed cc. ofacetic anhydride while in a third burette was placed a solution of 33.6g. of hexamine dissolved in 55 g. of acetic acid, 6 cc. of the ammoniumnitrate-nitric acid solution in the one burette was added to 30 cc. ofacetic acid and 30 cc. acetic anhydride (this amount is in addition tothe 150 cc.) in the reaction flask. Thereafter the remaining threeliquids in the three burettes were all added concurrently andequivalently. The reaction conditions and procedure were otherwisesimilar to those described in Example, IIL' 9 Certain aspects of theall-liquid-feed modifications of the present invention are moreparticularly described and claimed in the aforesaid application ofGeorge P. Wright, Douglas C. Downing and Henry H. Richmond, Serial No.495,082, filed July 16, 1943, issued as Patent No. 2,434,879, January20, 1948.

PURIFICATION The cyclonite produced in accordance with the presentinvention may be purified, if desired, either by recrystallization fromany convenient cyclonite-solvent, (for example, 70% nitric acid, 50%acetic acid, dioxane, monobutyl ether of ethylene glycol, nitromethane,acetone, and the like); or by digestion with dilute nitric acid in anamount insufficient completely to dissolve the crude material. Aparticularly advantageous method of etfecting the first-mentioned methodof purification (i. e., recrystallization) is more particularlydescribed and claimed in the copending application of Johnson, Blomquistand McCrone, Serial No. 495,081, both of which are filed on even dateherewith.

The second-mentioned method of purification (i. e., digestion withdilute nitric acid) is illustrated in the following example.

Example V (PURIFICATION) The first-crop material of Example I (meltingpoint 20l203 C. corr.) was stirred with 55% nitric acid at 70 C. forone-half hour, 25 cc. of nitric acid being used for every g. of crudecyclonite. During the digestion, some gas was evolved as the nitric acidattacked and destroyed oxidizable impurities. The digested mixture wasthen cooled and the solid filtered. A 96% recovery of high gradecyclonite, melting at 205-206 C., with no softening below 200 C., wasobtained. The second-crop material from Example I and II (which usuallycontains considerably more homocyclonite than first-crop material) mayalso be purified by digestion in a similar manner but with a somewhatlonger period of digestion. Likewise the single-crop product obtained inExamples III and IV (which is intermediate in purity between the firstand second-crop materials of Examples I and II) may be purified by thesame general procedure. If the digestion is carried out for severalhours (e. g., 6-7 hours) the crystals increase in particle size.

If desired, the filtrate from the digestion procedure may be used todigest further quantities of crude product. In some instances it mayalso be desirable to dissolve the crude cyclonite in 70% nitric acid andthen to dilute the solution to 55% nitric acid strength (thereby partlyprecipitating the material), before carrying out the diges tion.Regardless of the details employed, however, the digestion procedure maybe used to efiect a substantial improvement in the size and quality ofthe cyclonite crystals (where the starting material is inferior in thisrespect), and also to destroy many of the oxidizable impurities whichmay be present in the material prior to treatment. If it is desired tolower the acidity of the digested material, the product may be groundand di gested with a large volume of boiling water, or the aciddigestedproduct may be purified by recrystallization, for example, in accordancewith the procedure set forth in the above-identified copendingapplications.

Another method of purification which may be used, if desired, is todigest the crude cyclonite with hot water containing either a smallamount (e. g., 25%) of acetone, or a small amount (e. g., 1%) of abuffering agent such as sodium tetraborate or sodium perborate. Thus thecrude cyclonite may be poached at 75 C. for 3 to 6 hours with watercontaining 1% perborate. The thus purified material generally exhibitsan increased frothing point and melting point, and is neutral to methylred.

It will be apparent to those skilled in the art that the presentinvention has been described in great detail in the foregoingspecification and also that many variations may readily be made withoutdeparting from the spirit and scope of the invention. I therefore intendto be limited only in accordance with the following patent claims.

I claim:

1. A process of producing an explosive, which comprises reacting ahexamine compound selected from the group consisting of hexamine itselfand henamine salts, with an ammonia-yielding ammonium salt, concentratednitric acid and a lower fatty acid anhydride, the reaction being carriedout at a temperature above about 35 to 45 C.

2. A process of preparing cyclonite which comprises reacting a hexaminecompound selected from the group consisting of hexamine itself andhexamine dinitrate, with ammonium nitrate and concentrated nitric acidin the presence of a fatty acid anhydride, said reactants being usedapproximately in the proportions of two to four moles of ammoniumnitrate, four to six moles of con centrated nitric acid and six to eightequivalents of anhydride per mole of hexamine compound in the case ofhexamine itself, and approximately in the proportions of two to fourmoles of ammonium nitrate, two to four moles of concentrated nitric acidand six to eight equivalents of anhydride per mole of hexamine compoundin the case of hexamine dinitrate.

3. The process of claim 2 wherein said anhydride comprises aceticanhydride.

4. The process of claim 2 wherein said reaction is carried out at atemperature above about 3545 C. and below about 100 C.

5. A process of preparing cyclonite which comprises treating hexaminewith ammonium nitrate and concentrated nitric acid in the presence ofacetic anhydride, approximately in the proportion of 2.3 to 3.2 moles ofammonium nitrate, 4.5 to 5 moles of concentrated nitric acid and 6.8 to8 moles of acetic anhydride per mole of hexamine, said reaction beingcarried out at a temperature suflicient to effect the formation of morethan one mole of cyclonite per mole of hexamine.

6. The process of claim 5 wherein said reaction is carried out at atemperature above about 35 to 45 C. and below about 100 C.

7. The process of claim 5 wherein said reaction is carried out at 6075C.

8. The process of preparing cyclonite which comprises reacting hexarninedinitrate with ammonium nitrate and concentnated nitric acid in thepresence of a lower fatty acid anhydride, approximately in theproportions of 2.3 to 3.2 moles of ammonium nitrate, 2.4 to 2.8 moles ofconcentrated nitric acid and 6.8 to 8 moles of anhydride per mole ofhexamine dinitrate, said reaction being carried out at a temperaturesufficient to effect the formation of more than one mole of cycloniteper mole of hexamine dinitrate.

9. The process of claim 8 wherein said reaction is carried out at atemperature above about 45 C. and below about 100 C.

10. The process of claim 8 wherein said reaction is carried out at 60-75C.

11. A process of preparing cyclonite which comprises reacting hexaminewith ammonium nitrate and concentrated nitric acid in the presence ofacetic anhydride, approximately in the proportions of 2.3 to 3.2 molesof ammonium nitrate, 4.5 to 5 moles of concentrated nitric acid, and 6.8to 8 moles of acetic anhydride per mole of hexamine, the reaction beingcarried out at 60 to C.

References Cited in the file of this patent Bachmann et al.: JournalAmer. Chem. Soc., vol. 71 (1949), pp. 1842-1845.

1. A PROCESS OF PRODUCING AN EXPLOSIVE, WHICH COMPRISES REACTING AHEXAMINE COMPOUND SELECTED FROM THE GROUP CONSISTING OF HEXAMINE ITSELFAND HEXAMINE SALTS, WITH AN AMMONIA-YIELDING AMMONIUM SALT, CONCENTRATEDNITRIC ACID AND A LOWER FATTY ACID ANHYDRIDE, THE REACTION BEING CARRIEDOUT AT A TEMPERATURE ABOVE ABOUT 35* TO 45*C.